In the past, various designs of valve actuators have been employed to operate valves in a variety of uses. Typically, actuators encompass a housing and a shaft slidably mounted in the housing and connected to a piston. The housing has an inlet to admit hydraulic pressure on one side of the piston. On the other side of the piston, a spring is disposed which bears on the piston. The spring provides the necessary force to draw the shaft back into the actuator, thereby closing the valve (or opening the valve, depending on the design) when hydraulic pressure is relieved or lost on top of the piston. It has been desirable in past designs to ensure that there is preload in the spring when the hydraulic pressure on the piston is withdrawn such that the spring is still somewhat compressed from its relaxed state at the conclusion of the stroke. In prior designs, housings have to be built at least as tall as the spring in a relaxed state. Specially designed presses were then employed to compress the spring and add any necessary retaining springs or other members that would keep the spring from jumping out of the housing if the top cover plate were removed.
Prior designs of actuators involve a specific design of an actuator for a specific application. Accordingly, the shaft was sized depending upon the encountered loads affecting the gate in the valve which is to be connected to the actuator shaft. This type of design limited the usefulness of actuators insofar as it was desired to use a given actuator for a valve other than that for which it was initially specified. While the components in the actuator may be suitable for a variety of applications, the actuator shaft diameter requirements may change, depending on the application. The apparatus of the present invention provides adaptability to handle a variety of shaft diameters in an existing actuator body.
The apparatus of the present invention also allows for assembly and preloading of the spring without any special tools and without the housing attached to the bonnet.
Of interest in understanding the background of the invention is the hydraulic actuator model SWC made by Baker CAC.